Commercially marketed personal computers are generally equipped with an industry standard parallel port for driving a peripheral device such as a printer, plotter, or local area network (LAN) adapter, such as the Xircom Pocket LAN Adapter. Although such computers are usually capable of selectively driving, via software, multiple logical parallel ports, generally designated LPT1, LPT2, and LPT3, they frequently come equipped with only a single physical parallel port. The industry standard physical parallel port utilizes a 25 pin D shell female connector. A cable having a mating male connector is typically used to connect the computer parallel port to a peripheral device.
At any one time, a single parallel port can only control a single peripheral device. Thus, a computer equipped with only one physical parallel port can connect to only a single printer. In order to facilitate connection of the computer to multiple peripheral devices, various manufacturers have marketed switch boxes which enable a user to manually switch a single input port to any one of N output ports. Such switch boxes can functionally connect only one peripheral device at a time to the computer, so therefore only one such device can be active at a time. The user must manually toggle the switch box to select a new active connection.
Because certain peripheral devices, such as the aforementioned network adapter, must be accessible to the computer at all times, conventional manually operated switch boxes are not suitable for use with these devices.